Volume2 number 10October 1975 Nucleic Acids Research Evidence of altered histooe interactions, as investigated by removal of histones, in chromatin isolated from rat liver nuclei by a conventional method

It is shown that the release of the slightly lysine-rich histones f2a2 and f2b by 0.4 M ammonium sulfate from conven-tionally isolated chromatin is diminished in comparison to the lysed nuclei. The change in extractability is further demon-strated by the application of ethidium bromide. At a molar in-put ratio of 0.0 $ (moles ethidium bromide/moles nucleotide) and 0.4 M ammonium sulfate the slightly lysine-rich histones are released from the chromatin to 70- 80 % if the lysed nuclei are used. At 0.1 M ammonium sulfate ethidium bromide effected also a release of 50 % of histone f1. Comparable ef-fects could not be observed with chromatin prepared in a con-ventional way but instead a tendency towards loss of histone f3 in the presence of ethidium bromide was observed. IMTRODUCTIOK The question in how far chromatin preserves essential "native" features after isolation from the nuclei has received increas-ing attention (1-5) • In a previous paper we have shown that chromatin changes its transcription properties in the course of the isolation procedure (1). Prom this result we suggested that alterations of the DNA-protein interactions may arise during the isolation procedure of the chromatin from the nu-clei (1). Recently, we could show that the ability of histone f1 to be extracted by ammonium sulfate in the region between 0.1 and 0.4 M depends on the way by which chromatin was ob-tained from the nuclei (5). Prom this result we concluded that deterioration of histone f1-chromatin interaction occurs dux-ing the conventionally applied preparation methods. In the present paper we have investigated whether also the extrac-tability of the other histone types is changed after isolatio